1. The Field of the Invention
This invention relates to furnace peep sights and more particularly to that class of apparatus which provides double sight glass protection between the viewer and the interior of the furnace and embodies an apparatus capable of closing off the interior of the furnace from view from a position from without the furnace.
2. Description of the Prior Art
The prior art abounds with furnace peep sights. U.S. Pat. No. 2,387,133 issued Oct. 16, 1945 to C. Foster teaches a peep hole box, utilizing water cooling for purposes of maintaining the orifice of the box at a cool temperature. Such orifice is removeably covered by a pivotable cover plate which when pivoted away from the orifice permits access therethrough thus providing an orifice which may be protected with the glass plate, if desired, or may be suitable for the insertion of test probes or other devices. However, the Foster apparatus becomes totally useful in the event that the glass plate shatters or is not employed by enabling heated gases to emerge outwardly from the orifice despite the walls of the orifice being in a cooled condition.
U.S. Pat. No. 2,112,063 issued Mar. 22, 1938 to J. Blizard discloses a peep sight for furnaces having particular use in double walled furnaces wherein the cavity separating the walls is operated at high pressure levels. The Blizard peep sight includes an elongated passageway traversing the double walled chamber and having at the exterior end thereof a hatchway, which when opened, permits the user to peer into the chamber traversing passageway. Coupled to the hatch is a shaft which in turn has a plate affixed thereto. This plate extends between the end of the chamber traversing passageway and the entrance opening into the furnace. Thus, when the hatch is moved so as to open a viewer end of the passageway, the plate is positioned such that an opening therein is juxtaposed over the entranceway into the interior of the furnace. The Blizard apparatus unfortunately couples the interior of the furnace directly to the users eye, excepting for the capability of inserting a glass or mica plate at any location along the length of the communicating passageway or at the ends thereof. Obviously, replacement of the transparent plate becomes exceedingly difficult and if ruptured or cracked fails to provide protection to the eyes of the user.
U.S. Pat. No. 1,973,171 issued Sept. 11, 1934 to W. H. Jacobi describes a furnace peep sight in which a plurality of elements are separately pivotably adapted to cover an opening in the sight. One of such coverings comprises a solid plate, the other comprises a screen. If desired, one of the pivotable plates may be fabricated having a transparent rigid substance, such as heat resistant glass or mica. However, in the event the user is employing such a transparent rigid plate and the plate cracks or becomes broken, the users eye is immediately subjected to the interior high temperature gases emerging outwardly from the interior of the furnace and through such crack or broken transparent plate.